Franco-British plans for intervention in the Winter War
During the early stages of World War II, the United Kingdom and France made a series of proposals to send troops to assist Finland against the Soviet Union during the Winter War, which started on 30 November 1939. The plans involved the transit of British and French troops and equipment through neutral Norway and Sweden.
Source: Wikipedia — Franco-British plans for intervention in the Winter War (CC BY-SA 4.0)